As we head into earnings season, stock indexes are near record highs, but an unusually large share of companies have warned analysts that they may be disappointed.

That's not how things work these days. The companies that make up the Standard & Poor's 500 index are expected to increase first-quarter earnings 1.6% over last year, according to Thomson Reuters. Nevertheless, U.S. stock markets closed at all-time highs on Tuesday, further expunging their bear-market losses. And strategists at several big...